1) Field of the Invention
The present invention relates to an optical system for achieving simultaneous observation of a front-direction object and a substantially-lateral-direction object and close-up enlarged view observation of the front-direction object.
2) Description of the Related Art
Conventionally, there have been known optical systems that make it possible to achieve simultaneous observation of a front-direction object and a substantially-lateral-direction object. Of such optical systems, there have been known to have a configuration in which light from the substantially-lateral-direction-object side is caused to emerge from the image side after being reflected inside the optical system (See Japanese Patent Kokai No. 2008-309859, Japanese Patent Kokai No. 2008-309859). Here, “substantially lateral direction” is defined to include not only a direction right beside the optical system but also a diagonally front direction and a diagonally back direction in reference to the optical system.